The present invention relates to an apparatus and a method for estimating a level of wakefulness of a driver from displacements of the vehicle body in a lateral direction.
The development of techniques for preventing accidents attributable to a reduction in the wakefulness of drivers is one of important subjects from the viewpoint of safety, and various methods for detecting a reduction of wakefulness and alarming techniques associated therewith have been conceived and put in use.
In JP-A-2002-154345, the applicant has proposed a technique associated with estimation of wakefulness for allowing the level of wakefulness of a driver to be accurately determined in the presence of significant changes in the driving environment and vehicle speed.
According to the wakefulness estimating technique disclosed in JP-A-154345, displacements of a vehicle in the width direction are first detected as a time series; the displacements are subjected to frequency transformation to calculate the quantities of frequency power components; and an average value of the quantities of the frequency power components is calculated as the quantity of high frequency components. At the same time, a maximum value of the quantities of frequency power components within a predetermined frequency range including a stagger frequency exposed when the driver is at a low level of wakefulness is calculated as the quantity of low frequency components.
Then, the level of wakefulness of the driver is determined based on a wakefulness value that is equivalent to the ratio of the quantity of the high frequency components to the quantity of the low frequency components.
According to the above-described related technique, the wakefulness of a driver is determined to be low when the quantity of the high frequency components is small and the quantity of the low frequency components is great.
However, for example, on a highway between mountains and having successive curves in different winding directions, a driver who is at a normal level of wakefulness drives the car by turning the steering wheel to the left and right at relatively small steering angles. The turning of the steering wheel in such a case is likely to be extracted as a low frequency component used for determination of stagger, which can cause an erroneous determination.